Light emitting diodes (hereinafter referred to as LEDs), organic or inorganic ELs, and other devices exist as light emitters. A typical structure of a displayer, an LCD backlight or an LED for lighting, among these devices, is illustrated in FIG. 1. This is the following structure: a structure wherein a silver paste or silicone resin die-bonding agent 4 is used to die-bond an LED chip 2 onto external metal electrodes 5 inside a package having a reflecting case 1 made of a plastic or ceramic material to give a good reflectivity; the die-bonding agent 4 is cured so as to bond positive and negative electrodes of the LED chip to the external electrodes, respectively, through wires 6; a dispenser is used to inject a liquid sealing resin 3 thereinto; and then the sealing resin is cured.
The used LED chip is a chip in a single color such as R, G or B, a chip wherein these are combined with each other, or a chip giving some other luminous color, such as yellow. In the LED chip illustrated in FIG. 1, only the front surface thereof has electrodes, and the bonding thereof is attained through two wires. However, in an LED chip having front and rear surfaces having electrodes, respectively, the bonding thereof is attained through a single wire. The used wire(s) is/are (each) a gold line or aluminum line having a diameter of 25 to 30 μm. The sealing resin used therefor is an epoxy resin or silicone resin. When the material of the reflecting case is a plastic material, the material is PPA. When the material is a ceramic material, the material is Al2O3 or the like.
The refractive index of the silicone resin or epoxy resin for the sealing resin is about 1.5; therefore, when light emitted from the LED chip is taken out through the sealing resin, the light emitted in the LED chip is reflected on the interface between the sealing resin and the air so that all of the emitted light is not taken out for the following reason: as illustrated in FIG. 4, the light emitted in the LED chip 2 is reflected on the reflecting case 1, and a light ray 8 radiated into the sealing resin surface at an angle 9 of 41.8 degrees or more to the direction perpendicular to the surface is totally reflected on the sealing resin surface so that the light ray is not taken out.
Accordingly, low is the light output efficiency of any LED using a slim package (hereinafter referred to as an SPKG), which is frequently used for an LCD backlight or the like that includes an LED having the same basic structure as illustrated in FIG. 1. The light output in the case of making use of an SPKG wherein a blue chip made of InGaN showing a dominant wavelength of 460 nm is used is from 50 to 60% of the light output in the case of an LED wherein a TO-18 package illustrated in FIG. 2 is used while the same chip is used and the form of a sealing resin on the light taken-out side of the Leis a convex lens form.
Therefore, in order to improve the light output efficiency, a light scattering region in an irregular or uneven form has been hitherto formed in the surface of a sealing resin of an LED through which light is emitted. Japanese Patent Application Laid-Open (JP-A) No. 56-019686 discloses a method of making the surface of a sealing resin of an LED rough mechanically, a method of sealing an LED chip with a resin by use of a mold having a rough surface, a method of curing a sealing resin composition wherein a powdery filler is mixed with a transparent sealing resin for sealing an LED chip, and then etching a surface of the sealing resin composition with a solution wherein the filler can be dissolved, thereby making the surface rough, or some other method. JP-A No. 2002-368289 discloses a method of making fine irregularities in the surface of a sealing resin of an LED by laser ablation, and further JP-A No. 2003-234509 discloses a method of printing, on the surface of a sealing resin of an LED, a resin film wherein an irregular surface is separately formed.
These methods are not preferred since the methods make a process for producing an LED complicated. Thus, an LED has been desired which is produced through a process for forming irregularities more simply in its sealing resin surface.